TML transport condition assessment determines whether a solid bulk cargo can be shipped safely without the risk of liquefaction, in accordance with the IMSBC Code and SOLAS requirements. By measuring the Transportable Moisture Limit (TML), the Flow Moisture Point (FMP), and the actual moisture content of cargoes such as iron ore fines, nickel ore, bauxite, and mineral concentrates, shippers, carriers, and surveyors can verify compliance and prevent cargo shift, listing, and capsize incidents.
Technical Overview
The Transportable Moisture Limit (TML) transport condition assessment is a laboratory-based safety evaluation required for solid bulk cargoes that may liquefy during sea transport. Under the cyclic stresses generated by a vessel rolling and pitching, a saturated or near-saturated granular cargo can undergo a rapid buildup of pore water pressure. This causes the cargo mass to lose shear strength and behave like a viscous fluid, a phenomenon known as liquefaction. Liquefaction can trigger cargo shift, sudden listing, structural damage, and, in the worst cases, the total loss of the vessel and its crew.
The regulatory framework for this assessment is the International Maritime Solid Bulk Cargoes (IMSBC) Code, made mandatory under the SOLAS Convention. Cargoes susceptible to liquefaction are classified as Group A cargoes. Before loading, the shipper must declare the TML and the actual moisture content of the cargo, and the cargo may only be loaded when its moisture content does not exceed the TML. The TML itself is defined as 90% of the Flow Moisture Point (FMP), the moisture level at which a cargo begins to exhibit plastic flow behavior under dynamic loading, providing a built-in 10% safety margin.
A complete TML transport condition assessment typically follows a defined workflow: representative sampling of the cargo stockpile or consignment, group classification and particle size analysis, selection of the appropriate TML test method, laboratory determination of the FMP and TML, parallel determination of the natural moisture content, and finally a compliance verdict supported by test certificates suitable for cargo declaration and port inspection.
Testing Samples
Iron Ore Fines and Concentrates
Iron ore fines, sinter feed, pellet feed, concentrates, and filter cakes are classic Group A cargoes due to their fine particle size, high density, and residual moisture from beneficiation and dewatering processes. Sampling is generally performed in accordance with ISO 3082, and moisture determination follows ISO 3087. Blends of different ore types or sources should be treated as distinct cargoes, each requiring its own TML evaluation.
Nickel Ore and Laterite
Nickel ore and nickel laterite cargoes, commonly shipped from Southeast Asia, are clay-rich materials with high natural moisture contents. They are among the highest-risk Group A cargoes and have been implicated in numerous liquefaction casualties. Rigorous TML and moisture content verification is strongly emphasized by flag states, port states, and P&I clubs for these shipments.
Bauxite and Aluminium Ores
Following amendments to the IMSBC Code, most bauxite cargoes are now classified as Group A unless proven otherwise by testing. Bauxite presents a particular challenge because cargo temperatures during transport can be significantly elevated, so the dedicated Proctor/Fagerberg method C modified, conducted at elevated temperature, is commonly applied to reflect realistic transport conditions.
Base and Precious Metal Concentrates
Copper, lead, zinc, manganese, tin, chrome, and fluorspar concentrates are produced through grinding and flotation circuits and retain process moisture after filtration. Their fine particle size and moisture sensitivity make TML assessment a routine pre-shipment requirement for exporters, smelters, and traders.
Coal and Other Granular Cargoes
Certain coals are classified as both Group A and Group B, meaning they present a liquefaction hazard in addition to chemical hazards such as methane emission and self-heating. Other materials assessed under this program include mineral sands, ilmenite, pyrites, and various wet metallurgical by-products and tailings destined for sea transport.
Testing Items
The scope of a TML transport condition assessment covers the full chain of testing needed to demonstrate IMSBC Code compliance:
- Group classification of the cargo (Group A, Group A and B, Group B, or Group C) in accordance with the individual schedules of the IMSBC Code
- Determination of the Transportable Moisture Limit (TML)
- Determination of the Flow Moisture Point (FMP)
- Determination of natural Moisture Content (MC) by oven-drying methods
- Particle size distribution analysis by sieving, used to select the appropriate TML test method
- Atterberg limit testing (liquid limit and plastic limit) to characterize the plasticity of fine fractions
- Bulk density and stowage factor determination
- Angle of repose measurement where cargo-shifting behavior must be evaluated
- Compliance assessment comparing declared moisture content against the TML, with a clear pass or fail conclusion
All results are compiled into a bilingual-ready test report and certification package suitable for cargo declarations, charter party requirements, and inspection by port state control authorities.
Testing Methods
Sampling and Sample Handling
Representative sampling is the foundation of a valid assessment. Samples are taken from stockpiles, conveyors, wagons, or hold loading points following the sampling procedures of the IMSBC Code Appendix 2 and applicable standards such as ISO 3082 for iron ores. Samples are sealed in airtight moisture-proof containers immediately after collection and transported promptly to the laboratory to prevent moisture loss, which would otherwise bias the results.
Moisture Content Determination
The moisture content of the cargo is determined by drying representative subsamples in a ventilated oven at 105 degrees Celsius to constant mass, in accordance with ISO 3087 for iron ores, ASTM D2216, or equivalent procedures. The moisture content is expressed as a percentage of the wet mass of the sample and is directly compared with the TML for the compliance decision.
Flow Table Test
The flow table test is the most widely applied method for fine and relatively fine materials with a maximum particle size of approximately 7 mm, with any small oversize fraction removed before testing. A specimen is compacted in a conical brass mould on a standardized flow table apparatus and subjected to repeated controlled drops at successively higher moisture contents. The flow moisture point is identified as the moisture level at which the specimen develops visible plastic flow and deformation beyond the acceptance criteria, and the TML is then calculated as 90% of that value.
Penetration Test
The penetration test is suitable for fine to relatively fine materials, including many mineral concentrates, and is often preferred when flow table results are ambiguous. The specimen is compacted in layers into a cylindrical mould, subjected to standardized vibration, and the penetration of a ball-tipped indenter is recorded across a range of moisture contents. The flow moisture point corresponds to the moisture content at which penetration increases sharply, indicating the transition toward flow behavior.
Proctor/Fagerberg Test
The Proctor/Fagerberg test (PFT) uses Proctor-type compaction equipment to build a compaction curve and saturation curve for the material, and is applied to coarser cargoes and to materials such as coal and bauxite where other methods give inconclusive results. The flow moisture point is derived from the point at which the compacted specimen approaches saturation and rapidly loses strength. The dedicated variant known as method C modified was developed specifically for bauxite and involves testing at elevated temperature to reproduce the thermal conditions experienced during transport.
Method Selection Logic
Selection among the three methods is based on particle size distribution, material composition, clay content, and the behavior of the cargo during preliminary trials. Where a cargo does not conform to an existing IMSBC schedule, a full tri-modal assessment covering classification, TML, and supplementary properties is recommended so that the shipper can prepare a proper cargo declaration.
Applications
TML transport condition assessments are used throughout the bulk shipping supply chain by a wide range of stakeholders:
- Exporters, traders, and miners requiring TML and moisture certificates before loading Group A cargoes such as iron ore fines, nickel ore, bauxite, and concentrates
- Shipowners, charterers, and masters verifying cargo documentation and deciding whether a consignment is safe to load
- Independent surveyors and P&I clubs performing pre-shipment inspections and hold surveys in liquefaction-prone trades
- Port authorities and maritime safety administrations auditing cargo declarations and enforcing IMSBC Code compliance
- Steel mills, smelters, and cargo receivers validating the condition of inbound materials and planning stockpile drainage or drying when moisture levels approach the limit
- Engineers evaluating transportability of tailings, filter cakes, and other wet mineral by-products for multimodal logistics projects
FAQ
What is the difference between TML, FMP, and moisture content?
The Flow Moisture Point (FMP) is the experimentally determined moisture level at which a cargo begins to show flow behavior under dynamic loading. The TML is a regulatory limit set at 90% of the FMP to provide a safety margin. The moisture content is the actual water present in the cargo at the time of sampling, and it must remain below the TML throughout loading and transport.
How long are TML test results valid?
Under IMSBC Code provisions, the TML certificate should be dated not more than six months before the commencement of loading, provided the cargo source and characteristics remain unchanged. The moisture content certificate must be determined much closer to loading, with sampling normally required within seven days of, or at, the time of loading.
What happens if the cargo moisture content exceeds the TML?
The cargo must not be loaded. The shipper is required to drain, dry, or otherwise reduce the moisture content, and retesting is necessary to confirm compliance. Loading wet Group A cargo is one of the most serious violations of the IMSBC Code and has been the cause of multiple vessel losses.
How much sample is required for testing?
The required quantity depends on the maximum particle size and heterogeneity of the cargo, typically ranging from several kilograms for fine concentrates to tens of kilograms for coarser materials. Sampling must follow recognized incremental sampling plans so that the laboratory specimen is statistically representative of the entire consignment.
Which TML test method should be used for my cargo?
The flow table test suits fine materials up to about 7 mm, the penetration test suits fine to relatively fine concentrates, and the Proctor/Fagerberg test is applied to coarser cargoes and to coal and bauxite where other methods are inconclusive. The laboratory selects and justifies the method after reviewing sieve analysis results and the cargo schedule.
Can TML be assessed for inland or multimodal transport?
Yes. Although the IMSBC Code governs sea transport, the same liquefaction mechanics apply to rail wagons, barges, and truck loads subjected to vibration and shock. TML-based assessments are increasingly used to evaluate transport conditions for wet mineral products across entire multimodal logistics chains.